Soluble catalyst systems for the preparation of polyalk-1-enes having high molecular weights

ABSTRACT

Catalyst systems for the polymerization of C 2  -C 10  -alk-1-enes contain, as active components, 
     a) a metallocene complex of the general formula I ##STR1##  where M is titanium, zirconium, hafnium, vanadium, niobium or tantalum, X is halogen or C 1  -C 8  -alkyl, Y is carbon, phosphorus, sulfur, silicon or germanium, Z is C 1  -C 8  -alkyl, C 3  -C 10  -cycloalkyl or C 6  -C 10  -aryl, R 1  and R 2  are identical or different and are each C 1  -C 4  -alkyl, R 3  to R 6  are identical or different and are each hydrogen or C 1  -C 8  -alkyl, or two adjacent radicals R 3  and R 4  and R 5  and R 6  in each case together form a hydrocarbon ring system of 4 to 15 carbon atoms and n is 0, 1 or 2, and 
     b) an open-chain or cyclic alumoxane compound of the general formula II or III ##STR2##  where R 7  is C 1  -C 4  -alkyl and n is from 5 to 30. The novel catalyst systems are particularly suitable for the preparation of polyalk-1-enes having high molecular weights.

This application is a continuation of application Ser. No. 08/158,777,filed on Dec. 1, 1993, now abandoned, which is a division of Ser. No.07/900,427, filed on Jun. 18, 1992, now U.S. Pat. No. 5,290,434.

The present invention relates to catalyst systems for the polymerizationof C₂ -C₁₀ -alk-1-enes, containing, as active components,

a) a metallocene complex of the general formula I ##STR3## where M istitanium, zirconium, hafnium, vanadium, niobium or tantalum, X ishalogen or C₁ -C₈ -alkyl, Y is carbon, phosphorus, sulfur, silicon orgermanium, Z is C₁ -C₈ -alkyl, C₃ -C₁₀ -cycloalkyl or C₆ -C₁₀ -aryl, R¹and R² are identical or different and are each C₁ -C₄ -alkyl, R.sup. 3to R⁶ are identical or different and are each hydrogen or C₁ -C₈ -alkyl,or two adjacent radicals R³ and R⁴ and R⁵ and R⁶ in each case togetherform a hydrocarbon ring system of 4 to 15 carbon atoms and n is 0, 1 or2, and

b) an open-chain or cyclic alumoxane compound of the general formula IIor III ##STR4## where R⁷ is C₁ -C₄ -alkyl and m is from 5 to 30.

The present invention furthermore relates to a process for thepreparation of polymers of propylene with the aid of these catalystsystems and to the polymers obtainable by this process.

In addition to the insoluble Ziegler-Natta catalysts, soluble catalystssystems can also be used for the polymerization of alk-1-enes. Saidsoluble catalyst systems are complex compounds of metals of subgroups IVand V of the Periodic Table with organic ligands, which are used inconjunction with oligomeric aluminum compounds (EP-A 185 918, EP-A 283739 and GB-A 2 207 136). The complex compounds used in these catalystsystems contain, as organic ligands, generally cyclopentadienyl groupswhich form 1 bonds with the transition metal. Transition metal complexeswhich, in addition to organic ligands, also contain halogens bonded tothe metal atom are also frequently used as catalysts.

EP-A 284 708 and 316 155 and EP-A 355 447 describe soluble catalystsystems for the polymerization of alk-1-enes, in whichbis(cyclopentadienyl) complexes of metals of subgroup IV of the PeriodicTable are used as complex compounds, the two cyclopentadienyl ringsbeing bonded by an alkyl-substituted silicon, tin or germanium atom orby sulfur atoms. Transition metal complexes in which thecyclopentadienyl rings are substituted by alkyl and which contain, asfurther ligands, two halogens bonded to the transition metal may also beused. The oligomeric aluminum compounds preferably used are linear orcyclic alumoxane compounds of the general formula II or III.

With the aid of such catalyst systems it is possible to obtain polymersof propylene which have, inter alia, a relatively narrow molecularweight distribution. In contrast to polypropylene which is prepared byusing insoluble Ziegler-Natta catalysts, the molecular weights of thepolypropylenes obtained in this manner are substantially lower, so thatthey cannot be used for many applications where polymers havingmolecular weights of more than 100,000 are employed.

A possible method for increasing the molecular weights of polyolefins isto reduce the reaction temperature during the polymerization. Propylenepolymers having molecular weights of about 50,000 (M_(w)) are obtainablein this manner, for example in EP-A 355 447. In this measure, however,the increase in the molecular weights is associated with a substantialdecrease in the polymerization rate, ie. a substantial increase in thereaction time, so that the reduction of the reaction temperature has anadverse effect on the cost-efficiency of the production process.

It is an object of the present invention to overcome this disadvantageand to provide an improved soluble catalyst system which makes itpossible to prepare polyalk-1-enes with high molecular weights in a veryeconomical manner.

We have found that this object is achieved by the soluble catalystsystems defined at the outset.

According to the invention, metal complexes of the general formula I,where titanium, zirconium, hafnium, vanadium, niobium or tantalum areused as the central atom M, are used. In the metal complexes to be usedaccording to the invention and of the general formula I, the centralatom is bonded on the one hand via π bonds to substitutedcyclopentadienyl groups and on the other hand to further substituents X,which may be fluorine, chlorine, bromine or iodine or C₁ -C₈ -alkyl.Metallocene complexes of the general formula I in which M is zirconiumor hafnium and X is chlorine or bromine are preferably used.

Furthermore, the metal complex to be used according to the invention andof the general formula I contains, in addition to the central atom andits substituents and the substituted cyclopentadienyl groups, also abridge member (Z)_(n) Y, which bonds the two cyclopentadienyl groups toone another. Here, Y is carbon, phosphorus, sulfur, silicon orgermanium, Z is C₁ -C₈ -alkyl, C₃ -C₁₀ -cycloalkyl or C₆ -C₁₀ -aryl andn is 0, 1 or 2.

In the preferably used metallocene complexes of the general formula I, Yis carbon, sulfur or silicon, Z is C₁ -C₄ -alkyl and n is 2.

A further important component of the metal complexes to be usedaccording to the invention and of the general formula I are substitutedcyclopentadienyl groups. These each contain radicals R¹ or R² which areidentical or different and are each C₁ -C₄ -alkyl, in particular methyl,ethyl, isopropyl or tert-butyl. These cyclopentadienyl groups also havethe substituents R³ to R⁶ where R³ to R⁶ are identical or different andare each hydrogen or C₁ -C₈ -alkyl, or two adjacent radicals R³ and R⁴and R⁵ and R⁶ in each case together form a hydrocarbon ring system of 4to 15 carbon atoms. Metallocene complexes of the general formula I whosecyclopentadienyl groups have substituents R³ to R⁶ where R³ and R⁵ areeach C₁ -C₄ -alkyl and R⁴ and R⁶ are each hydrogen and two adjacentradicals R³ and R⁴ and R⁵ and R⁶ in each case together form ahydrocarbon ring system of 4 to 12 carbon atoms, for example an indenylsystem, are preferably used. The number of carbon atoms of thehydrocarbon ring systems includes the two carbon atoms of thecyclopentadienyl system which serve as linkage points with thesubstituents R³ to R⁶ so that, for example when R³ and R⁴ and R⁵ and R⁶are in each case cyclohexyl, there are altogether two hydrocarbon ringsystems, each of 6 carbon atoms.

Examples of particularly preferred metallocene complexes include

dimethylsilanediylbis-(2-methylindenyl)-zirconium dichloride,

diethylsilanediylbis-(2-methylindenyl)-zirconium dichloride,

dimethylsilanediylbis-(2-ethylindenyl)-zirconium dichloride,

dimethylsilanediylbis-(2-isopropylindenyl)-zirconium dichloride,

dimethylsilanediylbis-(2-tert-butylindenyl)-zirconium dichloride,

diethylsilanediylbis-(2-methylindenyl)-zirconium dibromide,

dimethylthiobis-(2-methylindenyl)-zirconium dichloride,dimethylsilanediylbis-(2-methyl-5-methylcyclopentadienyl)-zirconiumdichloride,

dimethylsilanediylbis-(2-methyl-5-ethylcyclopentadienyl)zirconiumdichloride,

dimethylsilanediylbis-(2-ethyl-5-isopropylcyclopentadienyl)-zirconiumdichloride,

dimethylsilanediylbis-(2-methylbenzindenyl)-zirconium dichloride and

dimethylsilanediylbis-(2-methylindenyl)-hafnium dichloride.

The synthesis of such complexes can be carried out by conventionalmethods, the reaction of the correspondingly substituted cycloalkenylanions with halides of titanium, zirconium, hafnium, vanadium, niobiumor tantalum being preferred. Examples of corresponding preparationprocesses are described in, inter alia, Journal of OrganometallicChemistry 369 (1989), 359-370.

In addition to the metallocene complex, the novel catalyst system alsocontains linear or cyclic alumoxane compounds of the general formula IIor III ##STR5## where R⁷ is preferably methyl or ethyl and m ispreferably from 10 to 25.

The preparation of these alumoxane compounds is usually carried out byreacting a solution of trialkylaluminum with water and is described in,inter alia, EPA 284 708 and U.S. Pat. No. A 4,794,096.

As a rule, the alumoxanes obtained are a form of mixtures of both linearand cyclic chain molecules of different lengths, so that m should beregarded as an average value. The alumoxane compound may also containtrialkylaluminumcompounds whose alkyl groups are each of 1 to 8 carbonatoms, for example trimethyl-, triethyl or methyldiethylaluminum.

In the polymerization of alk-1-enes with the aid of the novel catalystsystem, it is advantageous to use the metallocene complex a) and thealumoxane compound b) in amounts such that the atomic ratio of aluminumfrom the alumoxane b) to the transition metal from the metallocenecomplex a) is from 10:1 to 10⁶ :1, in particular from 10:1 to 10⁴ :1.The two catalyst components can be introduced into the polymerizationreactor individually in any order or as a mixture. A particularlyreactive soluble catalyst system is obtainable when the metallocenecomplex a) and the alumoxane compound b) are mixed with one another from5 to 60, preferably from 10 to 40, minutes before the actualpolymerization. The catalyst activated in this manner can then be usedimmediately.

With the aid of these soluble catalyst systems, it is possible toprepare polymers of alk-1-enes. These are understood as meaning homo-and copolymers of C₂ -C₁₀ -alk-1-enes, ethylene, propylene, but-1-ene,pent-1-ene and hex-1-ene preferably being used as monomers. The novelcatalyst systems are particularly suitable for the preparation ofpolypropylene and of copolymers of propylene with minor amounts of otherC₂ -C₁₀ -alk-1-enes, in particular of ethylene and but-1-ene.

The preparation of these polymers can be carried out in the conventionalreactors used for the polymerization of alk-1-enes, either batchwise or,preferably, continuously. Suitable reactors include continuouslyoperated stirred settles and a number of stirred kettles connected inseries may also be used.

The polymerization is carried out at from 0.1 to 3,000, preferably from0.5 to 2,500, bar and from -20° to 300° C. preferably from +10° to +150°C. The polymerization time is usually from 0.5 to 10 hours.

Polymerization reactions carried out with the aid of the novel catalystsystem can be effected in the gas phase, in liquid monomers or in inertsolvents. The polymerization in solvents, in particular in liquidhydrocarbons, such as benzene or toluene, is preferably used. In thiscase, it is advantageous if from 10⁻³ to 10⁻¹ mol of aluminumasalumoxane is used per liter of the solvent.

The average molecular weight of the polymers formed can be controlled bythe methods conventionally used in polymerization technology, forexample by the addition of regulators, such as hydrogen, or by changingthe reaction temperatures.

Polymers prepared with the aid of the novel catalyst systems have a highmolecular weight and a narrow molecular weight distribution. They canalso be prepared at relatively high temperatures, with the result thatthe polymerization time can be limited. Owing to these properties, thepolymers obtainable using the novel catalyst systems are particularlysuitable. for the production of films and moldings.

Examples for the preparation of polypropylene EXAMPLE 1

350 ml of dry toluene were initially taken in a stirred autoclave havinga useful volume of 1 L, and a solution of 0.45 g of methylalumoxane(average chain length m=20) in 30 ml of toluene was then added. 7.6×10⁻³mol of aluminum was used per-liter of the solvent. A solution of 15 mgof dimethylsilanediylbis-(2-methylindenyl)-zirconium dichloride(corresponding to 7.6×10⁻³ mol) in 15 ml of toluene was then added, sothat the atomic ratio of aluminum to zirconium was 244:1. This mixturewas first stirred for 30 minutes at 50° C, after which propylene wasforced in under a pressure of 2 bar and polymerization was carried outfor 4 hours and 40 minutes. The polymerization was effected at 50° C.and 2 bar. Thereafter, unconsumed propylene was removed and a mixture of1 L of methanol and 10 ml of concentrated hydrochloric acid were addedto the reaction solution. The precipitated polymer was filtered off,washed with methanol and dried under reduced pressure.

45 g of polypropylene having a weight average molecular weight (M_(w))of 114,200, a number average molecular weight (M_(n)) of 41,500 and amolecular weight distribution (M_(w) /M_(n)) of 2.75 were obtained.

EXAMPLE 2

The procedure was similar to that of Example 1, 350 ml of dry toluenelikewise being initially taken and a solution of 0.45 g ofmethylalumoxane (m =20) in 30 ml of toluene then being added.Thereafter, a suspension of 0.5 mg of dimethylsilanediylbis-3,3'-(2-methylbenzindenyl)!-zirconium dichloride in 20 ml of toluene wasadded, so that the atomic ratio of aluminum to zirconium was 8950:1. Thefurther procedure was then as described under Example 1.

51.4 g of polypropylene having a weight average molecular weight (M_(w))of 142,896, a number average molecular weight (M_(n)) of 91,917 and amolecular weight distribution of 1.55 were obtained.

Pentad content, measured by ¹³ C-NMR: amount mmmm=93.5%.

We claim:
 1. A process for the preparation of a polymer of a C₂ -C₁₀-alk-1-ene which comprises polymerizing a C₂ -C₁₀ -alk-1-ene at from 0.1to 3,000 bar and from -20° to 300° C. in the presence of a catalystsystem containing as active components,a) a metallocene complex which isdimethylsilanediyl-bis-(2-methylbenzindenyl)-zirconium dichloride and b)an open-chain or cyclic alumoxane compound of the formula II or III##STR6## where R⁷ is C₁ -C₄ -alkyl and m is from 5 to
 30. 2. A polymerof a C₂ -C₁₀ -alk-1-ene, obtained by the process as claimed in claim 1.